As one example of a wireless communication system to be improved by having the present invention apply thereto, 3GPP LTE (3rd generation partnership project long term evolution) (hereinafter abbreviated LTE) communication system is schematically described as follows.
FIG. 1 is a schematic diagram of E-UMTS network structure as an example of a wireless communication system. E-UMTS (evolved universal mobile telecommunications system) is the system evolved from a conventional UMTS (universal mobile telecommunications system) and its basic standardization is progressing by 3GPP. Generally, E-UMTS can be called LTE (long term evolution) system. For the details of the technical specifications of UMTS and E-UMTS, Release 7 and Release 8 of ‘3rd Generation Partnership Project: Technical Specification Group Radio Access Network’ can be referred to.
Referring to FIG. 1, E-UMTS consists of a user equipment (UE) 120, base stations (eNode B: eNB) 110a and 110b and an access gateway (AG) provided to an end terminal of a network (E-UTRAN) to be connected to an external network. The base station is able to simultaneously transmit multi-data stream for a broadcast service, a multicast service and/or a unicast service.
At least one or more cells exist in one base station. The cell is set to one of bandwidths including 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz and the like and then provides an uplink or downlink transmission service to a plurality of user equipments. Different cells can be set to provide different bandwidths, respectively. A base station controls data transmissions and receptions for a plurality of user equipments. A base station sends downlink scheduling information on downlink (DL) data to inform a corresponding user equipment of time/frequency region for transmitting data to the corresponding user equipment, coding, data size, HARQ (hybrid automatic repeat and request) relevant information and the like. And, the base station sends uplink scheduling information on uplink (UL) data to a corresponding user equipment to inform the corresponding user equipment of time/frequency region available for the corresponding user equipment, coding, data size, HARQ relevant information and the like. An interface for a user traffic transmission or a control traffic transmission is usable between base stations. A core network (CN) can consist of an AG, a network node for user registration of a user equipment and the like. The AG manages mobility of the user equipment by a unit of TA (tracking area) including a plurality of cells.
In order to improve performance of the related art LTE communication system mentioned in the above description, ongoing discussions are made on 5G communication technology. And, the 5G communication system is expected to use spatial modulation scheme based on massive MIMO technology.
FIG. 2 is a diagram showing a difference between spatial multiplexing and spatial modulation.
FIG. 2(a) is a diagram for explaining the spatial multiplexing scheme. According to spatial multiplexing scheme, different signals (S1 and S2) are transmitted via different transmission antennas. On the other hand, FIG. 2(b) is a diagram for explaining the spatial modulation scheme. According to spatial modulation scheme, S1 is transmitted via antenna 0 or 1, and selection of antenna 0/1 represents S2. That is, S2 can be represent not based on the signals transmitted via each antenna, but based on selection of antennas for transmission.
So, spatial modulation (SM) can be referred to as a single-RF multiple-antenna transmission technique. The smaller RF-chain number and low detection complexity at the receiver of spatial modulation make it an energy-efficient modulation method for the massive MIMO system. According to Massive MIMO scheme to be employed to 5G standardization technology, the targeted MIMO dimension may amount up to hundreds of antennas and the transmitter and receiver.
However, the above explained spatial modulation has a problem in that it may suffer antenna specific error. For example, when the channel of antenna 0 is poor in the example of FIG. 2(b), the transmission of S1 via antenna 0 might fail. So, the spatial modulation has to be modified to have spatial diversity gain.
Further, the transmission rate of spatial modulation is lower than spatial multiplexing scheme. For example, when there are Nt transmission antennas, and one symbol (S1) represents M information, the spatial multiplexing scheme can convey Nt log2 (M) bits for one transmission. On the other hand, for the same environment, spatial modulation scheme can convey log2 (Nt)+log2 (M) bit for one transmission.